Method of making electric resistance



Dec. 18, 1934. A. HAROLDSON 1,985,166

METHOD OF MAKING ELECTRIC RESISTANCE Filed May 1, 1950 Patented Dec. 18,1934 PATENT OFFICE METHOD or MAKING mo'mro aasrs'ranon Haroidson,Valparaiso, Ind assigno'r, by means assignments, to Continental Diamond:3? Company, Newark, Dei., a corporation a iiumion May 1, mo, Serial No.448,900 0m (01. sol-'11s) My present invention relates in general toelectrical conductor material particularly adapted for use in electricalresistance units.

The invention is particularly adapted for the 5 production of volumecontrols or fixed resistors particularly adaptable for radio apparatuswhere inexpensive but,accurate control of electrical cir-.'

cuits is important. The invention is also adapted for use in precisionrheostats and other resistance units used in electric circuits.

One of the objects of my invention resides in providing a method formaking resistors wherein the measuring of predetermined quantities ofthe conductive substance of which the unit is 16 composed isaccomplished in a simple and inexpensive manner, and wherein the same inits molded state is consolidated with a relatively thin base or carrierformed by means of a heat curable material. 7

Yet another object of my invention resides in the provision of aresistance unit made by the method herein disclosed.

These andother objects of my invention will be apparent from a perusalof the following speci- 26 fication when taken in connection with theaccompanying drawing wherein:

Figure 1 is a bottom view of one form of die by means of which the shapeand amount of conductive material may be applied directly to either 30 asheet of treated or untreated material;

Figure 2 is a perspective view showing a sheet of tissue paper impressedby the die shown in Fi ure 1; 1

Figure 3 is a view showing said strip of tissue 36 paper superimposedupon a sheet of heat curable material in its unreacted state;

1 Figure 4 is a view of the laminated finished material provided with anumber of the resistance units:

I 9, Figure 5'is a view similar to Figure 3 showing a manner in whichthe conductive materials are pressed by a die directly on a sheet ofuntreated thermo-plastic material but before the latteris heated andpressed to finished form;

Figure 6 is a perspective view of a resistor which is provided with agraduated carbon deposition made in accordance with my invention; and

Figure 7 is a side view of the same. In my improved method for forming aresist- 50 ance unit, I provide a die preferably of metal provided withone or more cavities of desired shape and cross section and adapted tocontain a predetermined and measured amount of conductive material.

, In the present instance, the die is illustrated as showing one or moreimpressions or cavities so that when impressed upon a sheet of materialit will form simultaneously one or more shapes thereon, all of which areidentical and each forming on the material impressed, a single or a se-5 ries of units, each containing a measured or predetermined amount ofsuch conductive material.

The conductive composition may include any type of conductive materialsuch as graphite, car 10 bon, aluminum, copper and the like, in finelydivided form. I prefer to use graphite or carbon, preferably in thecolloidal form. In the present instance I use colloidal graphite whichis known among the trade as "Aquadag. I may also form a suspension ofgraphite or carbon in amyl acetate or the conductor material may beformed as a water suspension in gelatin, together with a trace ofammonia as a binder for the powdered conductor so asto assist the finelydivided conductive material in retaining a substantially moldable formfor impressiori'or deposition upon the carrier.

Instead oi making single or multiple impressions from the die, I mayprovide a die of continuous and cylindrical construction to operateeither continuously orperiodically upon a strip or sheet of material fedin proximity to the die so that a continuous process may be afforded.The die is provided with means for intermittently or con-, tinuouslyfilling the impressions with conductive material and for scraping offthe surplus material so that each cavity will contain the same amount 01conductive material. This die is rotated or positioned so as tosuccessively deposit upon the periodically fed strip, a succession ofsuch deposits.

Inany case, in using either a single die or a rotary die, after thecavity in the die has been filled with the conductive material, thesurplus must be scraped off so as to have only a precise amount ofmaterial in the cavity whereby uniformity and accuracy in measurement issecured .for each of the die impressions.

In another aspect of my invention, the conducting material itself may bemixed with an insulating material in various proportions in order tovary the conductivity and resistance per unit length in the resultingmaterial. By properlycontrolling the ratio of conducting tononconducting material during manufacture, a material is maintainedhaving any desired resistance and conductive characteristics. However,in the present instance, the resistance unit is disclosed 8, be ngIormed of the conductive substance such as graphite or carbon withoutbeing admixed with a filler or insulating material.

In each instance, this conducting material will adhere to the cavitiesof the. die, but when the die is impressed to the sheet material, theconductive. material will pull away from the die and adhere to thesheet, due to the natural adhesive qualities of the paper or greateradhesive attraction between the substance and paper than between thesubstance and the metal die.

In this way, the measured amount of COD-7' ductive material of thedesired cross section and of the desired resistance is applied directlyto the sheet material or carrier, such as absorbent fibre paper of 5mils in thickness, or upontissue paper, either of which may be treatedor untreated with heat curable material inits unreacted state. In thepreferred manner of carrying out my invention, the die 2 carrying theone or more cavities i ls impressed directly upon the carrier strip, orsheetof thin paper, such as tissue-paper 6, thereby leaving thereon thecorresponding measured amounts of conductive ma terial 8 of the desiredcross sectional shape and configuration. After this has been done, thecarrier strip or sheet of thin paper carrying the strip of depositionsis superimposed upon a base 10 comprising a resin treated sheet orsheets of paper or fabric.

The sheet and base are then inserted in the usual press and subjected toheat and pressure whereby the tissue paper carrier and the base will beconsolidated and permanently and integraliyunited. During the moldingprocess, the heat curable resin will permeate the carrier strip and thedeposited resistor units so that in this manner, a cured strip ofBakelite will be formed having consolidated and molded in the surfacethereof a series of resistance units, each unit being of desired crosssectional shape and electrical characteristic. The separate units maythen be cut out and used in any desired manner.

Instead of depositing the resistor units on the carrier sheet of tissuepaper, I may apply them directly to the base as shown in Figure 5 of thedrawing, in which case the carrier sheet of tissue paper is dispensedwith and the resistance units will be directly and integrallyconsolidated with the base during the heat treating and pressingoperation.

In some instances I may die press the conductive units to an untreatedsheet to which a thermo-plastic resin can afterwards be applied, oralternatively, this untreated sheet may be superimposed on a Bakelite orresin-treated sheet so that the Bakelite of the second sheet willpenetrate the first sheet and bind them together to provide a laminatedbase or carrier to which the units are consolidated. In either case thesheets will then be treated with heat and pressure to consolidate theunits to the sheet or sheets.

It is to be understood that when I refer to sheets which are to betreated with "BakeI-ite or other resin compound, I include not onlypaper sheets, but also fabric sheets.

In certain instances, as shown in Figures 6 and 7, my inventioncomprehends the production of electric resistance material or a resistorwherein the resistance is controlled by the thickness of the graphite orcarbon deposited. For instance, in certain portions of the resistor, thegraphite or carbon is deposited relatively thick and as the resistancetapers off, the thickness of the deposition gradually decreases.Referring to Figures 6 and 7,. the same show a resistor or other elementmade in accordance with my invention comprising the base or carrier 10of resin treated sheet material with the resistor consolidated therewithin accordance with the method hereinbefore set forth. In this instance,the carbon, graphite, or other deposition 12- is of tapering orgraduated thickness, the end of the resistor at the left shown inFigures 6 and 7 being thicker with the deposition gradually thinningtoward the right, or toward the other end of the resistance element.-

In the same manner, my invention contemplates the provision of aresistor having different zones of its surface provided with crosssectional areas of conducting material of different thicknesses. This isof course controlled by the depth of the die cavity when the same isdeposited upon 'the sheet material, as hereinbefore described.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. The herein described method of forming units of the characterdescribed which includes pre-forming a measured amount of a'conductivesubstance to a desired form and cross section, impressing the sameupon'a very thin sheet in such a manner that the unit in its formedshape adheres directly to said sheet, applying said sheet to a secondsheet and consolidating said unit,-

said first sheet and said second sheet, by means of a resinous binderthrough the action of heat and pressure.

2. The herein described method of forming an electric unit of thecharacter described which consists of molding a measured amount ofelectrically conductive material to desired shape and cross section,impressing the same directly upon a sheet of tissue paper, applying thesheet of tissue paper to a sheet of material treated with phenoliccondensation product and applying heat and pressure thereto.

3. The herein described method of forming an electric unit whichconsists in filling the cavity of a die of predetermined shape and crosssection with a moldable electrically conductive material, passing ascraping instrument over the surface of the die to remove surplusmaterial and thereby leaving a measured amount of said material in thedie, impressing the die upon a sheet and superimposing said sheet upon asecond sheet and consolidating said two sheets and said substancepermanently by means of a resinous binder and under heat and pressure.

4. The process of making resistance units which includes the steps ofcausing an adherence of a preformed mass of moist particles ofresistance material having predetermined resistance characteristics toan absorbent carrier sheet to provide a combined unit havingpredetermined resistance characteristics, and embedding the combinedunit under heat and pressure in a base impregnated with an uncuredphenol condensation product.

5. The process of making resistance units which includes the steps ofpreforming a quantity of conductive material to a desired form, im-

pressing the same upon an absorbent carrier to cause adherence of theconductive material to said carrier, applying said carrier to a secondcarrier, and consolidating the composite struc-

